Epidermal growth factor (EGF) is produced in large amounts by the mouse submandibular gland. It is also present in such biological fluids as plasma, milk, urine and saliva. EGF is a potent mitogen for a wide variety of cells in culture but its function in the body needs to be elucidated. Our previous studies have demonstrated that EGF plays a key role in the development of the mammary gland during pregnancy and mammary tumorigenesis in female mice; in males it serves a role in spermatogenesis by stimulating the meiosis of spermatocytes. We have continued our studies to elucidate the physiological role of EGF by employing a variety of experimental approaches, including radioimmunoassay of EGF in tissues and biological fluids, EGF receptor assay and bioassay of EGF in cell culture. In addition, we have established the useful means of causing EGF deficiency in mice by removal of the submandibular gland and/or administration of anti-EGF antiserum. These procedures, combined with EGF replacement therapy have provided valuable information concerning the function of EGF in the body. Our studies have shown that the concentration of EGF in the submandibular gland and plasma of female mice increases significantly during pregnancy. Attentuation of the rise in EGF by sialoadenectomy and anti-EGF treatment resulted in increased rate of spontaneous abortion, suggesting that EGF is necessary for the normal course of pregnancy. In addition, EGF has been shown to have a physiological role in maintaining the normal structure of the epidermis. Our studies also have revealed that milk contains a high concentration of EGF which serves as physiological function by promoting neonatal eyelid opening.